Piston



C. E. SUMMERS May 2, 1933. PLATED PISTON Re. 18,814

Original Filed'Aug. Lo, 1930 gwuentoz Reissued May 2, 1933 UNITED STATES .Q QFFIC CALEB E. SUMMERS, OF PONTIAC, MICHIGAN, ASSIGNOR '10 GENERAL MOTORS COR- PORATION, OF DETROIT, MICHIGAN, A COBPOBATIGN.OF DELAWARE PLATED rrs'ron Original N0. 1,856,272, dated May 3, 1932, semi No. 474,935, filed August 18, 1930. Application for reissue filed September 21,

cation to the contacting areas of the cylinder or piston a relatively thin coating of a metal softer than the portions of the piston and cylinder which would otherwise normally ent is well known that, in commercial practice, cylinders are seldom perfectly round, and, even if made so, they become more-or less distorted by the temperature changes which they undergo. Pistons are also subject to similar defects and are even more liable to distortion by temperature changes because the head portion normally reaches a temperature several hundred degrees higher than the lower part of the skirt. It is therefore not feasible to produce commercially a piston that will fit the cylinded bore when cold and not be so tight as to cause seizing or scoring when hot.

In order to secure a fit sufficiently close for operative efiiciency, it is customary to assemble pistons in the cylinders with a closer fit than is possible for full speed operation and then operate the engine at low speed until the pistons have been run in by actual wear to a degree of looseness permitting full speed.

In accordance with the present invention I obviate, to a considerable extent, the difliculties hitherto encountered by applying to one of the surfaces to be engaged a thin coating of a metal sufiiciently soft and plastic to permit the coating to give way readily should the piston tend to seize. The coatin is pref erably so thin that it constitutes, in itself, no considerable body of metal and therefore does not assume the burden of maintaining the piston shape under the pressures and impacts incident to piston operation. The preferred thickness is in the neighborhood of only a thousandth of an inch although, of course, the thickness may be varied within the scope of the invention within limits measured in thousandths of an inch.

The metal employed for the coating should 1982. Serial No. 634,212.

surface. With pistons and cylinders of cast iron or other ferrous metal, soft and plastic metals such as copper, lead and tin may be mentioned as suitable. I prefer tin,however,

and have found it to give satisfactory results. 5

Notwithstanding its low melting point, it adheres strongly and wears comparably to the iron. I have found that tin, or alloys thereof having characteristics determined by the presence of the tin, are particularly suitable 6 for sliding engagement with ferrous metal surfaces because of their low coefiicient of friction and resultant high degree of antifriction qualities as hearing metals. This property is found to be a characteristic also of lead 5 and of some other metals and alloys thereof, for exam le, silver and cadmium.

'The so metal may be applied in any manner adapted to produce a coating of the thinness and evenness desired. A process of elec- 7 tro-deposition is preferred, such process enabling a very uniform coating to be applied to the entire bearing surfaces.

In the accompanying drawing, I have illustrated the application of the mvention to 7 an engine in which the bearing surfaces of the piston are coated with a softer metal. Referrin to the drawing, 1 indicates a. piston which may be of conventional character so far as sha e and material are concerned, 8 being prefera ly of cast iron. The walls of the cylinder are indicated at 2 and the soft metal coating at 3.

In applying the coating to the piston it may be most convenient to coat the entire ex- I tenor of the piston after which, if desired,. the coating may be removed from the ring grooves 4 by a finishing cut and from the piston pin bearings 5 by reaming.

-In'the use of pistons plated in accordance i with the present invention, b making the iron portion of the piston su ciently small so that there is no danger of scoring and then applying suflicient tin so that the piston enters the bore with a clearance of only i .0005 to .0015 inch, I have found it possible to operate the engine immediately at pracproper clearance at all ly generated.

In addition to the shortening of the slowspeed running in. period, by reason of the ease with which the coating forms itself to the bore, the invention permits of a tighter initial fit thereby lengthening the useful life of the piston. It also provides means whereby pistonsthat have become worn or are initially undersize may be fitted to the cylinder and whereby oversize pistons may be roduced to fit worn or oversize cylinders.

t also enables pistons and cylinders to be assembled with much less exact fitting and points is automaticalfinish than has hitherto been required while at the same time preventing seizing or scoring. Furthermore, the soft metal apparentl fills the pores of the cast iron of the cylindlar thereby rendering the surface smoother than it would otherwise be.

As an example of actual practicein the automobile industry, the following procedure is given: Pistons of cast iron for cast iron cylinders of 3 A to 3% inches bore are ground to such diameter that they wlll enter the cylinder with a clearance of three thousandths of an inch, or one and one-half thousandths on a side. This was the standard clearance for such istons before adoption of coating with so tmetal. In accordance with the present invention, the pistons are then coated with tin to a thickness of three quarters of a thousandth leaving the final clearance one and one-half thousandths of an inch as compared with the standard practice previously of three thousandths. The ring grooves are then turned and the head of the piston ground, leaving the plastic metal coating on the sides where the piston engages the cylinder.

Pistons so treated form themselves to the cylinder under operating conditions, the plastic metal accommodating itself to the slight and unavoidable irregularities of the con'ugate surfaces. At the same time, notwithstanding the closer fit, the danger of seizure or sticking up of the pistons is practically eliminated as the plastic metal will yield at points of highest pressure before suflicient heat and pressure are developed to cause the piston to seize.

It has been proposed, heretofore, to provide a piston with relatively thick bands or rings of Babbitt metal bearing upon the cylinder surface. Such construction, however, would not offer the advantages found in the present invention since the soft metal bands receive the full pressure and impact incident to engine operation and are subject to distortion, overheating and rapid wear. A coating of only a few thousandths of 'an inch applied to the cast iron of the piston skirt, in addition to have the advantages pointed out above, difiers from theprior suggested practice in that the very th n caat g is unaffected by high temperatures and is ri id ly and directly backed up and supporte by the piston body so that no material change in form of the bearing surface takes place except as a result of the running in process or subsequent normal wear. It also provides a more extended bearin surface than even the cast iron alone won (1 have so that the load is taken by an oil film over a greater area thereby distributing the friction which would 'otherwise result from concentrated loads where the cast iron contacts on relatively small areas.

I claim:

1. The combination with a cylinder and piston having cooperating surfaces of ferrous metal of a coating integrally united with one of said surfaces consisting of a thin layer of a metal of high anti-friction bearing qualities and sufliciently plastic to yield at the areas of greater pressure during the operation of the parts to thereby prevent seizing of the piston.

2. Structure as set forth in claim 1, said coating being predominantly of tin.

3. A piston for internal combustion engines comprising a body portion of ferrous metal having on the surfaces designed to contact with the cylinder Wall an integrally joined thin coating of relatively soft metal of high anti-friction bearing qualities and sufiiciently plastic to. yield at pressures at which the piston would tend to seize.

4. Structure as set forth in claim 3, said coating being of electrolytically deposited tin.

.5. The combination with a cylinder and piston having cooperating surfaces of ferrous metal, said piston fitted to said cylinder with usual clearance, of a coating of relatively soft metal integrally joined to the wearing surface of said piston, said coating being of suflicient thickness to reduce the clearance to approximately one and one-half thousandths of an inch.

6. Structure as set forth in claim 5, the coating being of electrolytically deposited tin.

7. A piston for internal combustion engines comprisinga cast iron body and acoating of tin on the cylinder-engaging surfaces of said body, said coating being of less than five thousandths of an inch in thickness.

8. The combination with a cylinder and piston having cooperating surfaces of relatively hard metal of a character subject to seizing and scoring due to temperature changes, of a coating integrally united with one of said surfaces consisting of a thin layer of metal of high anti-friction bearing qualities and sufficiently plastic to yield at the areas of greater pressure during the operation of the parts to thereby prevent seizing of the piston in the cylinder.

9, A piston comprising a portion of relatively hard metal having on the surfaces designed to contact with the cylinder wall an integrally joined thin coating of relatively soft metal of high anti-friction bearing qua ities and sufiiciently plastic to yield at pressures at which the piston would tend to seize.

10. A piston for internal combustion engines comprising a relatively hard metal body and a coating of tin on the cylinder-engag- 1 ing surfaces of said body, said coating being of less than five thousandths of an inch in thickness.

In testimony whereof I afiix my si ature.

CALEB E. S ERS. v 

